Field of the Invention
The present invention relates generally to ink-jet technology and, more particularly to a heated printing zone vacuum platen. p 2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in OUTPUT HARDCOPY [sic] DEVICES, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). As providing background information, the foregoing documents are incorporated herein by reference.
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, xe2x80x9cvacuum induced forcexe2x80x9d is also referred to as xe2x80x9cvacuum induced flow,xe2x80x9dxe2x80x9cvacuum flow,xe2x80x9d or more simply as just xe2x80x9cvacuumxe2x80x9d or xe2x80x9csuction,xe2x80x9d as best fits the context.] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve hard copy apparatus throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum through the drum cylinder provides a suction force at the holes in the drum surface (see e.g., U.S. Pat. No. 4,237,466 (Scranton)). [The term xe2x80x9cdrumxe2x80x9d as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term xe2x80x9cplatenxe2x80x9d can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, such as the ubiquitous typewriter rubber roller; thus, for the purposes of the present application, xe2x80x9cplatenxe2x80x9d is used generically for any shape paper holddown surface used in a hard copy apparatus.] Permeable belts traversing a vacuum inducing support have been similarly employed (see e.g., Scranton and U.S. patent application Ser. No. 09/163,098 by Rasmussen et al. for a BELT DRIVEN MEDIA HANDLING SYSTEM WITH FEEDBACK CONTROL FOR IMPROVING MEDIA ADVANCE ACCURACY (assigned to the common assignee of the present invention and incorporated herein by reference)).
Generally in a hard copy apparatus implementation, the vacuum device is used either to support cut-sheet print media during transport to a printing station of a hard copy apparatus, to hold the sheet media at the printing station while images are formed (known as the xe2x80x9cprinting zonexe2x80x9d), or both. [In order to simplify discussion, the term xe2x80x9cpaperxe2x80x9d is used hereinafter to refer to all types of print media and the term xe2x80x9cprinterxe2x80x9d to refer to all types of hard copy apparatus; no limitation on the scope of the invention is intended nor should any be implied.]
Typically thermal ink-jet inks are water based and when deposited on wood-based papers, they are absorbed into the cellulose fibers, causing the fibers to swell. As the cellulose fibers swell, they generate localized expansions, causing the paper cockle. Not only does this create a finished hard copy product that may be objectionable to the end-user, cockle growth can cause actual degradation of ink dot printing quality itself due to uncontrolled pen-to-paper spacing which may even, in turn, lead to pen printhead-to-paper contact as the cockle waves move a region of the paper upwardly.
Moreover, most commercial ink-jet printers allow the paper to exit the printing zone on a flat platen or into a substantially flat output tray while the ink is drying. A flat platen with no post-printing holddown mechanism allows cockle to expand, generally creating larger waves in the sleet of paper.
Furthermore, in order to produce high quality color copy, e.g., photo-quality printing, ink flux is increased to produce vivid color saturation. This flux increase further exacerbates the paper cockle problem.
Still further, ink-jet printhead size is increasing to increase throughput. As the print zone length increases, ink bleed effects and the paper cockle problem are again enlarged or intensified.
Several solutions to these problems have been developed. U.S. Pat. No. 4,329,295 (Medin et al.) for a PRINT ZONE HEATER SCREEN FOR THERMAL INK-JET PRINTER, U.S. Pat. No. 5,461,408 (Giles et al.) for a DUAL FEED PAPER PATH FOR INK-JET PRINTER, U.S. Pat. No. 5,399,039 (Giles et al.) for an INK-JET PRINTER WITH PRECISE PRINT ZONE MEDIA CONTROL, U.S. Pat. No. 5,420,621 (Richtsmeier et al.) for a DOUBLE STAR WHEEL FOR POST-PRINTING MEDIA CONTROL IN INKJET PRINTING, and Des. Pat. No. 358,417 (Medin et al.) (each is assigned to the common assignee of the present invention and incorporated herein by reference) exemplify various techniques for a hard copy apparatus using conventional electromechanical paper feed systems. U.S. Patent No. 5,742,315 (Szlucha et al.) shows a SEGMENTED FLEXIBLE HEATER FOR DRYING A PRINTED IMAGE. A segmented flexible heater is disposed adjacently to a paper path for heating a recording medium before and during printing.
There remains a need for print zone and post-print zone paper path transport mechanisms that assist in reducing the expanding paper cockle problem. One solution is to hold the paper to a platen with a vacuum force during printing. However, it has been found that with vacuum holding creates a higher frequency, or xe2x80x9csharperxe2x80x9d looking, cockle wave in the paper. The geometric complexities of designing a vacuum transport type apparatus compounded by the heating of the transported flexible material creates a need for improved heat distribution mechanisms. In ink-jet printing applications, there is a need for vacuum holddown paper path systems that assist in reducing or substantially eliminating paper cockle.
In a basic aspects the present invention provides a print media vacuum holddown device, including: supporting mechanisms for supporting a print media transport belt, having a first pattern of vacuum passages therethrough for distributing vacuum across a support surface, the support surface having a second pattern of surface mechanisms for containing heating mechanisms interspersed with the first pattern of vacuum passages; and heating mechanisms for generating heat for transmission to the belt, wherein the heating mechanisms are inset within the surface mechanisms such that the heating mechanisms are substantially surrounded by a gap from the supporting mechanisms wherein the supporting mechanisms is insulated from heat emitted by the heating mechanisms.
In another basic aspect, the present invention provides a hard copy apparatus, including: a printing station; proximate the printing station, writing mechanisms for printing on print media; transport mechanisms for selectively transporting the print media into and out of the printing station; and mounted proximate the printing station adjacently to the writing mechanisms, vacuum platen mechanisms for supporting print media transported through the printing station, the platen mechanisms including supporting mechanisms for supporting a print media transport belt, having a first pattern of vacuum ports therethrough and a support surface having a second pattern of surface channels interspersed with the first pattern of vacuum ports, and heating mechanisms for transmitting heat to the belt, inset within the surface channels such that the heating mechanisms are substantially surrounded by a gap from the supporting mechanisms wherein the supporting mechanisms is insulated from heat emitted by the heating mechanisms.
Another basic aspect of the present invention is a method for heating a print medium in a printing zone of a hard copy apparatus having a vacuum inducing subsystem, including the steps of: providing a vacuum holddown and positioning the holddown in the printing zone; interspersing electrical heating elements with vacuum ports across a surface of the holddown such that the heating elements are isolated from the surface by a gap; and transporting the print medium through the printing zone on a belt in superjacent contact with the platen at least in the printing zone while reducing cockle from ink droplets deposited on the medium and heat loss via the vacuum subsystem.
In another basic aspect, the present invention provides a method for heating on a print medium in a printing zone of a hard copy apparatus having a vacuum inducing subsystem, including the steps of: positioning a vacuum holddown having an electrically resistive, heat emitting surface in the printing zone, the surface have passageways therethrough coupled to the vacuum inducing system; and transporting the print medium through the printing zone on a belt in superjacent direct contact with the surface at least in the printing zone, using the surface for reducing cockle from ink droplets deposited on the medium while reducing heat loss via the vacuum subsystem.
Some advantages of the present invention are:
it reduces the spread of thermal mass and therefore the attendant amount of energy and time to bring a heater tip to operating temperature;
it reduces the loss of thermal energy through the vacuum platen structure itself due to the intrinsic air flow design;
it substantially eliminates thermal mass induced lang and resultant non-uniform temperature profiles in the printing zone;
it reduces spreading of undesirable heat to adjacent parts of the hard copy apparatus and vacuum subsystems;
it uses materials conducive to faster rise time to operating temperatures;
it provides a vacuum transport for ink-jet paper transport which will reduce cockling;
it reduces or substantially eliminates thermal expansion induced problems; and
it limits heat loss through the vacuum subsystem and the concomitant need for more powerful and efficient heating subsystems, thus reducing cost of manufacture.
The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprize the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches.
Other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.